Objectives: 1. Develop immunologic and ultrastructural techniques for examination of surface antigens and receptor sites on human leucocytes and on tumor cells. 2. Study effects of overt and covert infections of viruses on the distribution and types of surface receptors on leucocytes and other cells. Major Findings: Hybrid antibody labeling technique has been developed to localize viral antigens in cultured cells. Proposed Course: Hybrid antibody method of immunolabeling for electron microscopy has been developed in our laboratory. System will be applied to tumor antigens and to virus infected cells.